A Cleaner Future
Tenneco Automotive, the world's largest manufacturer of OE and replacement exhaust systems and components - known under the Gillet and Walker brand names respectively - has introduced catalytic converters fully compatible with cars equipped with OBD (on-board diagnostic systems) to be ready when these become mandatory as original equipment in 2001. In addition, the company is confident that it will be able to meet the demand for replacement OBD-compatible cats. Other developments emerging from Tenneco Automotive's continuous programme of innovation include new catalytic converters for diesel and GDI engines utilising revolutionary technology to reduce nitrous oxide emissions.
OBD continuously monitors the performance of all emission-related components in a car. If a problem is detected an MIL (Malfunction Indicator Lamp) illuminates on the dashboard to alert the driver to the situation and a fault code is recorded by the engine management computer. That code can then be read by a mechanic, using a diagnostic tool, and the problem rectified. Under a recently-introduced EU Directive aimed at further reducing vehicle emissions, motor manufacturers have to include OBD on all petrol-engined vehicles seeking type approval during 2000, for production from 2001, and on diesel cars seeking type approval in 2002. Tenneco Automotive started work on OBD for its aftermarket division in 1997 and even earlier for the car manufacturers.
Through its OE division, Gillet, Tenneco Automotive is working with a number of motor manufacturers to develop a range of OBD-compatible catalytic converters. OBD constantly tests the efficiency of catalytic converters by monitoring their oxygen storage rate.
The major difficulty in developing a compatible catalytic converter is that the relation between a cat's oxygen storage capacity and its conversion efficiency varies according to an individual vehicle's different load characteristics, and the system must be engineered to accurately indicate loss of conversion under these differing conditions, so that it can be triggered to each vehicle's individual characteristics. An additional lambda sensor has been introduced behind the converter, so that the system can measure the oxygen present before and after the emissions enter the catalyst. While the cat is operating correctly, its oxygen storage capacity will be high and consequently the lambda signal behind the converter will be low. However, as a catalytic converter fails, its oxygen storage capacity falls. The two lambda signals begin to equalise, triggering the MIL and the recording of a fault code. The new Walker range of OBD-compatible replacement cats, which will be available in 2002/2003, will feature the same technology.
Reducing nitrous oxide emissions for diesel and GDI vehicles
Although vehicle pollution has fallen dramatically since the compulsory introduction of catalytic converters to all new cars in 1992, nitrous oxide emissions, the major contributor to acid rain, low-level ozone and smog, remain a significant problem. These emissions can be efficiently reduced in petrol engines with a rich air/fuel ratio, using a three-way catalytic converter with ECU.
However, diesel engines require a very lean air/fuel mixture, making it difficult to effectively reduce the NOx produced. Tenneco Automotive with its Gillet and Walker products, working in conjunction with Siemens, is developing a new system to reduce these emissions in diesel vehicles.
To date, NOx emissions in diesel engines have been controlled by a two-way catalytic converter which oxidises CO and HC, used in conjunction with an exhaust gas recirculating system to enrich the air/fuel ratio, consequently reducing NOx emissions. Tenneco Automotive's new SiNOx system will reduce the NOx emissions even though the air/fuel mix is very lean. The system comprises two converters - one which oxidises CO and HC, and a second, denox cat, which produces an injection of urea which reacts immediately with the exhaust gas to form ammonia, a reducing agent for nitrous oxides.
GDI-engined vehicles also present the same problem, as they, too, require a very lean mix. Tenneco Automotive is developing a new system, comprising a converter to oxidise CO and HC, and a second which stores NOx when the air/fuel mix is lean. This reduces the NOx during periods of fast acceleration or when the vehicle is fully loaded, when the air/fuel mixture becomes richer and NOx emissions can be reduced efficiently. This system will incorporate a heat exchanger, as the oxidising converter has a higher operating temperature than the new denox cat.
Faster light-off times
Another area of concern that Tenneco Automotive is addressing is that of light-off times; the time taken for a catalytic converter to reach the temperature it needs to work effectively (around 300°C).
Until that temperature is reached, the car's emissions are high in CO and HC. The light-off time can be unacceptably long, particularly from a cold start or in cold weather.
With the introduction of the latest European Emissions Standard, Euro III, has also come a change in the way emissions are measured for pollutants. Until now, measurement began only after the engine had started and idled for 40 seconds.
Now, the measurement begins the moment the engine is switched on and, because as much as 90% of pollutants are emitted before light-off is reached, this is a far more severe test. Accordingly, to further reduce emissions, Tenneco Automotive is working to reduce light-off times, by introducing electrically pre-heated catalysts, airgap insulation, close-coupled converters and a tubular manifold. This should bring the time to light-off down to just a few seconds.
A satisfying challenge
Presently, Tenneco Automotive produces under its Walker brand, 220 different catalytic converters, for over 1300 applications, and this figure is set to increase. Juan Carlos Diez, Product Manager for Catalytic Converters for Walker said "Our aim isn't simply to meet the emission reduction standards established by new EU legislation. More than 40 specialists are employed in our development centres at Edenkoben, Germany and in a number of satellite centres, and we constantly set ourselves the challenge of finding the most efficient solution to the problem of vehicle pollution.
Every time we meet that challenge and add a new converter to our range, we have the satisfaction of knowing that we are helping the environment. We are committing tremendous resources to ensure that we continue to innovate."